The purpose of the proposed research is to determine if regenerative treatment of class II furcation defects will result in predictable, clinically significant, amounts of bone fill and closure of the furcation defects. Long term follow up of periodontal treatment, indicates that periodontal lesions that have advanced into the furcation area in between the roots of multi-rooted teeth have a much higher tooth mortality rate, over time, than do other treated periodontal lesions. This lower success rate of therapy in furcation lesions may be explained by the anatomical inaccessibility of these areas which interferes with successful debridement during treatment procedures as well as the patients daily hygiene attempts. During a series of years we have investigated the possibility of bone regeneration and closure of furcation defects in dogs. We have developed regenerative therapies that will predictably close dog furcation defects. These techniques have recently been adapted to human use, in preliminary studies, with successful closure of a number of human furcation defects via bone regeneration. However, the predictability of this therapy needs to be determined before it can be recommended as a treatment alternative for furcation lesions. In the proposed study, 90 human furcation defects will be treated with regenerative peridontal surgery which will include citric acid conditioning of the debrided furcation site and coronal repositioning of the surgical flap margin for adequate wound closure to allow proper healing of the surgical site. The soft tissue changes of the treated areas will be determined from measurements of probing depth, probing attachment level, and location of the gingival margin. The hard tissue changes will be determined from measurements of probing bone level ("bone sounding") and form direct bone probing at surgery and at surgical reentry after 12 months. In addition bone fill, expressed in terms of defect volume and bone closure of the defects (+ or -), will be evaluated using reproductions of the defects in die stone, obtained by taking impressions of the sites at initial surgery and at 12- month reentry. Evaluation of the results will allow determination of the predictability of bone fill and closure of the furcation defects. Predictable bone fill with closure of the defects will provide a long sought for therapy in these difficult treatment areas.